The loading of a shopping cart with bags of groceries presents the danger of delicate groceries being crushed. Although skillful cart loaders are careful to put the hard, heavy objects, such as food cans, in first, there is always the danger that during cart movement the cart contents will rearrange themselves, resulting for example in a loaf of bread being crushed between two bags of food cans. Another danger is that of having bag contents spill out onto the bottom of the cart. This is a particular problem with the plastic store bags of today, with their very flexible sides. Not only must the contents be re-bagged prior to loading the bags into a car, but the loose groceries make it more difficult to find a spot for placing subsequent bags on the cart bottom surface.
Moreover, for some shoppers, the amount they purchase per shopping trip is limited to how much can be loaded into a standard-size shopping cart. Finding some way of loading more onto a standard-size shopping cart would increase the purchases such a shopper would make on a shopping trip, thereby benefiting the store merchant who made this possible.
Another purpose towards which shopping carts are employed is to provide a mobile working station for store employees evaluating inventory, or performing other related tasks. Store employees sometimes rest a tray on top of a shopping cart, in order to provide a working surface for themselves. This is an imperfect solution, however, as the tray may not be affirmatively retained on the cart top, and may threaten to tilt off at any moment.